This invention relates to liquid crystal displays (LCDs) with integrated touch panels, and more particularly, to LCDs with integrated touch panels that prevent sensor malfunction by eliminating coupling noises.
A wide variety of display devices capable of displaying images are known, including cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma display panels (PDPs), and so on. In such display devices, a touch panel may used as an input means adapted to sense a location on a display screen to which pressure is applied, and a user of the touch panel can thereby easily enter data by touching the display screen with a pen, a finger, or the like.
In order to address issues relating to the thickness or size of a touch panel, new types of LCDs with integrated touch panels are currently being developed. In these, efforts are being made to reduce the thickness of the touch panel, which is an advantageous feature in manufacturing thin LCDs. In addition, since it is not necessary to assemble separate modules, these new LCDs are particularly effective in increasing production yields.
In an LCD having an integrated touch panel, a common electrode formed on a common electrode panel comes into contact with a sensor electrode formed on a thin film transistor (TFT) array panel in response to external pressure of a finger or the like, so that a predetermined voltage is applied to a sensor line and then provided to a sensor so as to output a signal having a specific level.
However, in this arrangement, a common voltage distortion can occur due to coupling between a data line formed on the TFT array panel and the common electrode formed on the common electrode panel. Whenever a data voltage is applied to a data line, the common voltage becomes severely distorted. Accordingly, the distorted common voltage is provided to the sensor through the sensor line, and since the sensor determines the polarities of two signals, that is, a reference signal having a specific level and a signal derived from the distorted common voltage, the polarities may be erroneously determined. Consequently, even when no external pressure is being applied to the touch panel, it may erroneously report the application of an external pressure. Moreover, when an external pressure is being applied to the touch panel, it is difficult to determine a coordinates signal that is indicative of the actual position corresponding to that external pressure.